Air heater and dust collector



May 12, 1959 e. F. DAVEY 4 AIR HEATER AND DUST COLLECTOR Filed Oct. 26,1955' I '2 Sheets-Sheet 1 l5 :1 I 4/10 1 20% I o I i v I H l4- I9 I r Il6 3 5m uvmvrox.

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y 1959 G. F. DAVEY 2,886,294

AIR HEATER AND DUST COLLECTOR Filed Oct. 26, 1955 2 Sheets-Sheet 2INVENTOR. GERALD F. DHVEY United States Patent AIR HEATER AND DUSTCOLLECTOR Gerald F. Davey, Holden, Mass., assignor to Riley StokerCorporation, Worcester, Mass., a corporation of MassachusettsApplication October 26, 1955, Serial No. 542,851 4 Claims. (Cl. 257-1)This invention relates to an air heater and dust collector and, moreparticularly, to apparatus arranged to heat combustion air entering asteam generating unit by bringing the air into heat exchangerelationship with flue gases leaving the unit and to remove flyash anddust from the flue gases.

It is common practicein the art of generating steam for power purposesto increase the efficiency of the steam generating unit by heatingincoming combustion air by passing it in heat exchange relationship tothe outgoing flue gases, whereby the flue gas temperature is lowered andheat loss up the stack is reduced at the same time that the combustionair is preheated to a desirable amount. Although there are many types ofheat exchange apparatus in which this process may take place, the mostdesirable from the standpoint of initial cost and of maintenance is theso-called tubular air heater in which the flue gases pass internally oftubes, while the incoming combustion air passes over the outer surfacesof the tubes. However, one drawback of the tubular air heater is that itis subject to corrosion. This corrosion generally takes place at theportion thereof in which the coldest combustion air comes in heatexchange relationship to the coldest flue gases. It is in this part ofthe air heater that the conditions of temperature exist which promotethe condensation of certain corrosive agents in the flue gas, the mostprominent of these being sulphuric acid. It has been noted, also, thatin the portions of the air heater which are subject to corrosion, thereare substantial deposits of flyash. There is considerable reason tobelieve that the deposits of flyash act as agents, to absorb thecondensed sulphuric acid in the manner of a blotter, and thus hold thecorrosive agent in contact with the tube walls; otherwise, the corrosiveacids would be re-evaporated by the scrubbing action of the gasespassing through the tubes and no corrosion, or little corrosion, wouldtake place. Attempts in the past to reduce this flyash accumulation,however, have had little effect, and there is a great need in the fieldfor a means of discouraging the deposits of flyash on the tube walls.Apparatus for removing dust from the flue gas and depositing it in ahopper or the like have been complicated and expensive. The presentinvention satisfied this need in a novel manner.

It is, therefore, an outstanding object of this invention to provide anair heater wherein deposits of flyash and the like on the heat exchangesurfaces are maintained at a minimum, while the flyash is taken out ofthe flue gas in a more desirable location.

It is another object of the invention to provide a tubular air heaterhaving means for scrubbing the internal walls of the tubes to assureoptimum heat exchange between flue gases flowing within the tubes andcombustion air flowing over the exterior surfaces of the tubes.

A still further object of the present invention is the provision of ameans for reducing flyash accumulation within the tubes of a tubular airheater, and increasing it in a more desirable location which means isinexpensive to manufacture, requires a minimum of maintenance, and

2,886,294 Patented May 12, 1959 which may be applied to existing airheaters with a mini mum of difficulty.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

The character of the invention, however, may be best understood byreference to certain of its structural forms as illustrated by theaccompanying drawings in which:

Figure 1 is a general view of a steam generating unit embodying theprinciples of the present invention,

Figure 2 is an enlarged view of a portion of the apparatus shown inFigure 1,

Figure 3 is a sectional view of an air heater and dust collectorconstructed accordingto a modified version of the invention, and

Figure 4 is a sectional view of an air heater showing a still furthermodification of the invention.

Referring first to Figure 1, wherein is shown the general features ofthe invention, a steam generating unit, indicated generally by thereference numeral 10, is shown as comprising a furnace 11 and a boiler13 of the usual type, the furnace having burners 12 mounted in the frontwall. An air heater and dust collector 14 is mounted to receive fluegases originating in the furnace 11 and passing through the boiler 13.The air heater is mounted rearwardly of the steam generating unit, has agas entrance chamber 15 mounted in communication with the back pass ofthe boiler 13 and has an exit chamber 16 which is connected to the stocknot shown, by means of a breeching 17. A forced draft fan 18 isconnected to the air heater to introduce air into the system. The airheater 14 is of the tubular type and consists generally of a lower tubesheet 19 and an upper tube sheet 20 joined by tubes 21. As is best shownin Figure 2, a wire 22 passes centrally through each of the tubes 21.The upper end of the wire passes through an upper wall 23 of the airheater and is held in a fixed position thereby. As is evident in thedrawing, the upper end of the wire is threaded and a nut 24 is passedthereover, there being a washer 25 inserted between the nut 24 and thewall 23. Because of the fact that the tubes 21 are vertical and the wall23 is slightly inclined to horizontal, the washer 25 is wedge-shaped.The threaded end of the wire 22 is exaggerated in the drawings to showthe manner in which the nut is mounted thereon. The lower end of thewire 22 passes through a lower duct wall 26 and has its extreme endthreaded to fit a nut 27. In this case the wall 26 is very greatlyinclined to horizontal so that a washer 28 having an extreme wedge shapeis used between the nut 27 and the wall 26. The wa1126 may be formed asa hopper to receive an accumulation of flyash. The Wire 22 is of veryhigh quality, being formed of stainless steel or other non-corrosivetype of metal and being drawn with a very smooth finish. A type of wirewhich will operate very well in this situation is music wire. The nuts27 and 24 are drawn up so that the wire is stretched tightly between thewalls 23 and 26.

The operation of the invention will now be clearly understood in view ofthe above description. Gases originating in the flame produced by theburners 12 leave the furnace 11 and pass through the boiler 13. Thesegases leave the boiler at a considerably reduced temperature, but thereis still considerable heat left in them. The gases enter the chamber 15and pass downwardly through the tubes 21 internally thereof, passingoutwardly through the chamber 16 and the breeching 17. Combustion air ithe incoming combustion air. After being preheated,

aseaaaa the. combustion air passes to the burners 12 where it' is usedin the combustion process. The gases passing downwardly through thetubes contain a number of materials. They contain for one thingcorrosive gases which condense at a fairly high temperature. When thesegases reach the point in the tubes 21 where they are about to bedischarged into the chamber 16, they are at their lowest temperaturebecause of the fact that the incoming combustion air is passing overthat section of the tubes. This is true because of the general practiceof flowing the com bustion air in counterflow to the flue gases so thatthe coldest combustion air is heated by the coldest flue gases. At thispoint the situation is ideal for the deposit of corrosive. liquids orcondensates on the walls of the tubes. At the same time the flue gasescontain fine particles of unburned ash, and if the walls of the tubesare made wet by the condensation of acids and the like on the surfacethereof, the flyash has a tendency to stick and, in many cases, theyform a deposit which eventually plugs the entire tube so that nothingcan pass through. In ad.- dition to plugging the tubes and increasingthe resistance of the air heater as a whole, these ashes act as holdersfor the corrosive liquids and serve to promote corrosion. However, whenthe nuts 24 and 27 have been tightened up properly, each of the wires 22is permitted. to vibrate at a frequency determined by the tension andthe size of the wire. With a proper adjustment, the wire will beresonant to a frequency which is to be found in the flue gases and willvibrate with a very great displacement. With a proper selection of wiresize and tension, the amount of displacement of these vibrations will beexact- 1y suificient to maintain the walls of the tubes clean andpolished without any substantial wearing of the wire itself. As a matterof fact, it has been noted that the vibration of the wire in an aircurrent causes a flow of current along the wire so that flyash will bedeposited at the lower end of each wire. This has been noted inparticular in the case of guy wires in old style biplanes where asubstantial deposit of dust is always to be found on the lower wingsurrounding the entrance of the wire therein at the lower end of thewire. Since all flue gases contain acoustical vibrations, it will not bedifficult in any given case to select a wire and a proper tension tomaintain the tubes in a condition which is free of flyash, andtherefore, to a great extent free of corrosion.

In Figure 3 is shown another manner in which the principles of thepresent invention may be carried out. In this case an air heater 34contains tubes 35 mounted between an upper tube sheet 36 and a lowertube sheet 37. A wall 38 resides in spaced relationship to the uppertube sheet 36 and defines therewith a gas entrance chamber 39. In asimilar manner a wall 40 resides in spaced relationship to the lowertube sheet 37 and defines therewith a gas exit chamber 41. A wire 42formed of noncorrosive material and drawn with a smooth surface finishresides generally centrally of each tube 35. The tube 42 hangs suspendedfrom the wall 38, its upper end being threaded and having a nut 43threaded thereon. A wedge-shaped washer 44 resides between the nut 43and the wall 38 to compensate for a slight inclination of the wall 38and to assure that the wire is mounted vertically. At the lower end ofthe wire 42 is mounted an aerodynamic member 45, which in thisembodiment of the invention is shown as a hollow cone formed with anotch 46' in its lower edge to promote spinning and off-center movement.The wire is connected to the apex of the cone. The operation of thisembodiment of-the invention isvery similar to that of the constructionshown in Figure 2. The flue gases entering the chamber 39 and passingdownwardly through the tube 35 to the exit chamber 41 invariably containcertain. acoustical vibrations. These flue gases striking theaerodynamic chamber cause it to move sideways because of its nonsymmetrical construction. This combined with the pulsations in the fluegas sets up vibrations in the wire 42 and with a proper selection ofwire of length, and of weight of aerodynamic member, the vibration willbe sufiicient for a displacement such that the walls of the tubes willbe kept clean and polished. As indicated in dotted lines, the wire atany given time will have nodes and anti-nodes along its length, but asis well known, these nodes and antinodes pass up and down on the wire sothat every portion of the surface of the tube will be polished by thewire at frequent intervals.

In Figure 4 an air heater 54 is shown as comprising a series of tubes 55extending between an upper tube sheet 56 and a lower tube sheet 57. Awall 58 resides in spaced relationship to the upper tube sheet 56 anddefines therewith a gas entrance chamber 59. A similar wall 60 lies inspaced relationship to the lower tube sheet 57 and defines therewith agas exit chamber 61. Between the walls 58 and 60 extends a wire 62formed of non-corrosive material and drawn with a very smooth surface.The lower end of the wire 62 passes through the wall 60 and is threadedto receive a nut 63. Between the nut 63-and the wall 60 resides a washer64 which is formed with inclined upper and lower surfaces to compensatefor the fact that the wall 60 is inclined to horizontal and to insurethat the wire 62 is held in absolutely vertical relationship axially ofthe tube 55. At its upper end the wire 62 passes through the Wall 58centrally of an aperture 65. Fastened over the aperture 65 is adome-shaped'diaphragm 66 formed of rubber or similar resilient materialwhich has centrally thereof a metallic plate bonded to the rubber andthrough which plate the upper end of the wire 62 passes. The wire iswelded to the plate 67 and is integral therewith. The outer edges of thediaphragm 66 are held to the wall 58 at the edges of the aperture 65 bymeans of an annular clamping plate 68 held to the wall 58 by fasteningmeans not shown. At its upper end the wire is provided with a weight 69.It will be understood then that with a proper selection of wire size andmaterial with a proper tension on the nut 63 and with the proper weight69, the wire 62 will vibrate at resonant frequency to a dominantacoustical vibration inthe flue gases passing through the tube 55. Atresonant frequency the wire will vibrate to polish and keep clean theinner surface of the tube and thereby reduce flyash accumulations whilecausing them to exist at the foot of each wire. Furthermore, forcedvibrations may be set up in each wire by striking the weight 69; forinstance, a stream of water from a hose may be sprayed over the top ofthe air heater occasionally to set the wires in motion.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

1. An air heater and dust collector for use with a furnace comprising afirst tube sheet, a second tube sheet spaced from the first, a firstwall spaced from the first tube sheet and defining therewith an entrancechamber adapted to receive flue gas from the furnace, a plurality oftubes extending between the tube sheet and adapted to receive the fluegases from the entrance chamber, a second wall spaced from the secondtube sheet and defining therewith an exit chamber adapted to receive theflue gases from the tubes, a wire of corrosion-resistant materialextending through each tube generally axially thereof, and meansmounting the wire for substantial vibration within the tube, the size ofthe wire being selected so that the nodes of vibration extend adjacentthe surface ofthe tube to prevent the accumulation of material thereon.

2. An air heater and dust collector for use with a 'furnace comprising afirst tube sheet, a second tube sheet wall and at the other end to thesecond wall, the ends of the wire extending through the walls and beingthreaded to receive nuts for determining the tension in the wireextending between the walls, the size of the wire being selected so thatthe nodes of vibration extend adjacent the surface of the tube toprevent the accumulation of material thereon.

3. An air heater and dust collector for use with a furnace comprising afirst tube sheet, a second tube sheet spaced from the first, a firstwall spaced from the first tube sheet and defining therewith an entrancechamber adapted to receive flue gas from the furnace, a plurality oftubes extending between the tube sheets and adapted to receive the fluegases from the entrance chamber, a. second wall spaced from the secondtube sheet and defining therewith an exit chamber adapted to receive theflue gases from the tubes, a wire of corrosion-resistant materialextending through each tube generally axially thereof, one end of thewire extending through the first wall and being threaded to receive anut, and an aerodydynamic member attached to the other end of the wire,

of tubes extending between the tube sheets and adapted to receive theflue gases from the entrance chamber, a second wall spaced from thesecond tube sheet and defining therewith an exit chamber adapted toreceive the flue gases from the tubes, a wire of corrosion-resistantmaterial extending through each tube generally axially thereof, one endof the wire extending through the second wall and being threaded toreceive a nut thereon, the other end of the wire extending through thefirst wall and being supported at the wall against substantial lateralmovement, and a weight attached to the said other end of the wire, thesize of the wire being selected so that the nodes of vibration extendadjacent the surface of the tube to prevent the accumulation of materialthereon.

References Cited in the file of this patent UNITED STATES PATENTS535,664 Bott Mar. 12, 1895 2,233,066 Watson Feb. 25, 1941 FOREIGNPATENTS 488,876 Germany Ian. 9, 1930 553,753 Great Britain June 3, 1943

